Wide Bandwidth and Low Driving Voltage Vented CMUTs for Airborne Applications

This paper presents a novel method to increase the bandwidth (BW) of airborne capacitive micromachined ultrasonic transducers (CMUTs). This method introduces a gaseous squeeze film as a damping mechanism, which induces a stiffening effect that lowers the pull-in voltage and improves the sensitivity....

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Bibliographic Details
Published in:IEEE transactions on ultrasonics, ferroelectrics, and frequency control ferroelectrics, and frequency control, 2019-11, Vol.66 (11), p.1777-1785
Main Authors: Ma, Bo, Firouzi, Kamyar, Brenner, Kevin, Khuri-Yakub, Butrus T.
Format: Article
Language:English
Subjects:
5G mobile communication
Acoustics
Artificial intelligence
Capacitive micromachined ultrasonic transducers (CMUTs)
Damping
Design parameters
Electric potential
Frequency control
Iron
low driving voltage
Micromachining
multi-parameter optimization
multiple hard-mask microfabrication
Nondestructive testing
Optimization
Sensitivity
squeeze film
Stiffening
Thermal imaging
Three-dimensional displays
Transducers
Trenches
Ultrasonic transducers
Voltage
wide bandwidth (BW)
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Summary:This paper presents a novel method to increase the bandwidth (BW) of airborne capacitive micromachined ultrasonic transducers (CMUTs). This method introduces a gaseous squeeze film as a damping mechanism, which induces a stiffening effect that lowers the pull-in voltage and improves the sensitivity. The optimal behavior of this stiffening effect versus the damping mechanism can be controlled by creating optimized fluidic trenches of various heights within the gap. The fractional BW can be controlled from 0.89% to 8.1% by adjusting the trench height while lowering the pull-in voltage to less than 54 V at the gap height of 1.0 μm. To achieve the largest sensitivity and lowest pull-in voltage at a given BW, we have developed a multi-parameter optimization method to adjust all combinations of design parameters. A novel multiple hard-mask process flow has been developed to enable fabrication of CMUTs with different cavity and trench heights on the same wafer. These devices provided an equivalent noise pressure level of 4.77 μPa/√Hz with 6.24-kHz BW for 7.6-μm deep fluidic trenches and 4.88 μPa/√Hz with 7.48-kHz BW for 14.3-μm deep fluidic trenches. This demonstration of the wide-BW CMUTs with high sensitivity and low pull-in voltage makes them applicable to medical and thermoacoustic imaging, nondestructive testing, and ultrasonic flow metering.
ISSN:0885-3010
1525-8955
DOI:10.1109/TUFFC.2019.2928170